Answer: 1 cup of coffee cost $1.15
Explanation:
Let x represent the cost of 1 breakfast sandwich.
Let y represent the cost of one cup of coffee.
Sue went to lunch and bought 1 breakfast sandwich and one cup of coffee for $2.10. This means that
x + y = 2.1 - - - - - - - - - - - - - -1
Jim bought 3 breakfast sandwiches and 2 cups of coffee for $5.15. This means that
3x + 2y = 5.15- - - - - - - - - - - - 2
Multiplying equation 1 by 3 and equation 2 by 1, it becomes
3x + 3y = 6.3
3x + 2y = 5.15
Subtracting, it becomes
y = 1.15
Substituting y = 1.15 into equation 1, it becomes
x + 1.15 = 2.1
x = 2.1 - 1.15
x = 0.95